This invention relates to an apparatus for applying a coating to a surface of a substrate at a constant coating thickness.
A conventional roll coater is shown in FIG. 3. The conventional apparatus includes a lower roller 1, and an associated upper roller 3 which are rotated while clamping therebetween a substrate 2 to be coated. A coating 5 is supplied to a surface of the upper roller 3 from a feeder 4 for applying the coating 5 to the upper roller 3, and the coating 5 applied by the feeder 4 is coated on the surface of the upper roller 3 at a uniform thickness to form a coating layer 7 by using a doctor 6. The upper roller 3 rotates on the substrate 2 with the coating layer 7 being applied onto the surface of the substrate 2.
In the conventional apparatus, the coating 5 applied on the surface of the upper roller 3 by the feeder 4 is likely to be piled, because the coating 5 applied by the feeder 4 spreads onto a flank or escape surface, i.e., the surface opposite to a rake surface 6a of a doctor 6. Therefore, the coating accumulated on the flank surface of the doctor 6 will drop onto the surface of the substrate 2 so that the coating dropped onto the substrate is adhered thereto in the form of an undesired protrusion.